Without some context and a description of the test conditions, I’d accept those as nothing more than numbers on a page.
How Good is the Clarity?
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Without some context and a description of the test conditions, I’d accept those as nothing more than numbers on a page.
David Towle
Well-Known Member
My normal daily driving is very similar each day. I've found under my conditions you can get about 2 mpg better (typically from 52 to 54 for me) by alternating HV Charge with EV. Most of the time my speed range is 35-50 mph. But this is a very limited range of conditions, Honda does not recommend using HV Charge at low speeds, and if you use it on the highway you are giving up the advantage of direct drive so I doubt there is any advantage there. I would only use it on the highway if I was low on charge and heading for mountains.
I think the improvement is due to the engine running continuously versus turning on and off all the time.
But I didn't do any of this for long since it was clear that EV driving is about 1/4 the cost of gasoline driving where I am.
Robert_Alabama
Well-Known Member
@Landshark ... A couple of graphs that might at least help you believe that what has been described is possible. At low power demands in HV mode, the engine may be running at low RPM and on a relatively low power output. Increasing the power requirement of the engine by turning on HV Charge may increase RPM and increase the engine loading, both of which could increase engine efficiency if it doesn't move beyond the sweet spot on the RPM curve (looks like it may be something like 2600 to 2800 RPM for the engines in the first graph).
This graph is for a diesel engine, but it shows the principle - the colors are efficency contours. Increasing RPM and increasing engine loading causes an increase in efficiency, up to a point (note the sweet spot of RPm at 2000 to 3000 and torque above 150 Nm - area inside red contour):
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Will EDM not engage while the vehicle is in HV Charge mode?
David Towle
Well-Known Member
Of course not it is running at too high an rpm for direct drive.
David Towle
Well-Known Member
Agreed efficiency could be part of that tiny mpg improvement also, but as I said on the highway it is likely negated by losing the ability for direct drive. Generating the electricity then using the electricity in the motor probably has a 10-15% inherent loss.
I don't drive enough on the highway to do a highway comparison of HV Charge/EV versus HV, , somebody who has a daily highway commute might be able to get some data over many runs.
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What is the RPM range under which the vehicle will operate in EDM? I’ve been in EDM up to 85mph, however, I have no way to measure RPM’s.
Robert_Alabama
Well-Known Member
I don’t think anyone mentioned 60 mpg. I’ve gotten above 50 mpg a bunch of times with the car and some of those times using HV charge at least some of the time.
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Typos fixed. Here’s the reference to 60mpg. You actually quoted it in bold letters.
Robert_Alabama
Well-Known Member
Touché. I interpreted it it as a range, not as an expectation or average, but yes it does reference 60mpg. I don’t think it was meant in the same context that you used it, however. I’ve worn myself out on this, but I maintain it is feasible to burn less gasoline selectively using HV Charge under the right conditions and I believe I’ve accomplished it, but proving it isn’t overly important to me. Again, I was once strongly on the same side of the argument as you, but I no longer take that side. I do believe blindly using HV charge a lot of the time isn’t smart for economics, though.
David Towle
Well-Known Member
I doubt there is a specific rpm range for gear drive. It should be limited by whether or not the engine can produce enough hp to drive the car at the rpm set by the fixed gear ratio. Going to electric drive is like a downshift, the engine can rev higher at a given speed and produce more hp to keep up with the aerodynamic load. I've only been up to 85 mph a few times, for me at that speed the car was in EDM less than 80% of the time. Its more like 95% at 75 mph (non EDM time at that speed is just the uphills for overpasses). And if you add to the load like using AC or going up a real hill the percent EDM time will go down much more.
David Towle
Well-Known Member
And as I said I agree, but I only found about 2 mpg more at a limited range of speeds. So is it worth bothering with? NO.
Robert_Alabama
Well-Known Member
I generally just attempt this when I want to add a few more miles to the battery setpoint and want to use HV Charge in the most economical manner (usually when on a trip when I can't recharge), so I agree that chasing this all the time isn't worth it. I won't take issue with the 2 mpg that you mention, but I think I probably got 4 mpg added the last time I used it like this, 2 mpg is certainly a safer estimate for expectations.
To the point of EDM not engaging while in HV Charge mode, have you read any Honda documentation that supports that claim? Have you reached that conclusion based solely on your observations?
I haven’t used HV Charge more than a handful of times and it’s probably been a year or more since the last time it was deployed. When I have, it has been at freeway speeds of 60-75mph. I can’t say with 100% certainty, but I may have observed the car being in EDM while in HV Charge.
One other observation is that there seems to be a delay from the time HV Charge is engaged and when actual charging begins to occur. That might suggest using HV Charge for brief periods, when conditions appear to be ideal, may be a fool’s errand.
David Towle
Well-Known Member
Yes just on my observations, its never gone into EDM when I have used HV Charge. And I've used it many times. Yes it could be just my car.
I also think at times the car's use of EDM is a fool's errand, on undulating roads it goes in and out of EDM so often it can't be doing any good. Cold temps or AC make it even worse. Even on mostly flat roads it goes in and out more often than it should, such as on the downhill side of every highway overpass on an otherwise flat road.
Fast Eddie B
Well-Known Member
I rarely used HV Charge - it seemed more efficient in principle to just hang onto one's desired EV range by using HV as appropriate.
On a few occasions, I did play a game to see exactly how many miles I could eke out of the battery, letting EV miles go to zero and then using HV Charge to get back to 5 or 10 miles of EV range, mainly to avoid angry bees. In those cases the EV range would sit on zero for a surprisingly long time, then suddenly jump up to 2.5 or 2.7 miles all at once. I assumed it was actually building up EV miles that whole time, but there was an algorithm not to show the miles until they met a certain threshold. But again, just my assumption.
I have observed the same thing after engaging HV Charge at zero EV miles. Similarly, I have crested summits in HV with zero EV miles, then switched to EV for the descent and experienced the same phenomenon.
Another type of delay has been observed by monitoring the Power Flow screen when HV Charge is initiated when there are 3 or more bars (some EV range) remaining on the battery gauge. The screen will show the engine running but no charge flowing to the battery. The delay can be a minute or two on a cold engine and perhaps 10-30 seconds on a warm engine. This might suggest that switching in and out of HV Charge rather than just leaving it on under the recommended conditions, would introduce some level of inefficiency to the system.
I’ve posted this graph before, but it may be worth another look. EDM operates within a very narrow window of torque and it must be within that window at a certain speed as well. Both conditions must be met. Similar to holing a putt in golf.
Isn’t it true that south of Orlando, the highest point in Florida is a freeway overpass? Even on a slight down hill stretch, or at some other point where it might not be expected, one of the conditions, most likely torque, will not exist and the vehicle will disengage from EDM. Heck, it might even go into EV Mode for a few seconds.
David Towle
Well-Known Member
Haha yes, and yes it does go into ev mode for a few seconds if using the cruise control. It is possible much of the time to avoid leaving EDM going down the overpass by increasing speed, but obviously this is normally not worth the hassle.
One variable I don't see on the graph is temperature, which was a huge factor for EDM engagement when I lived up north. EDM would only engage maybe 30% of the time for many ski trips to Vermont. Or maybe low temperature is just increasing the required torque and thereby moving out of EDM range?
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